GETOPT(3)						     Linux Programmer's Manual							 GETOPT(3)

NAME

       getopt - Parse command line options

SYNOPSIS

       #include <unistd.h>

       int getopt(int argc, char * const argv[],
		  const char *optstring);

       extern char *optarg;
       extern int optind, opterr, optopt;

       #define _GNU_SOURCE
       #include <getopt.h>

       int getopt_long(int argc, char * const argv[],
		  const char *optstring,
		  const struct option *longopts, int *longindex);

       int getopt_long_only(int argc, char * const argv[],
		  const char *optstring,
		  const struct option *longopts, int *longindex);

DESCRIPTION

       The  getopt()  function	parses	the command line arguments.  Its arguments argc and argv are the argument count and array as passed to the
       main() function on program invocation.  An element of argv that starts with `-' (and is not exactly "-" or "--") is an option element.  The
       characters  of  this element (aside from the initial `-') are option characters.  If getopt() is called repeatedly, it returns successively
       each of the option characters from each of the option elements.

       If getopt() finds another option character, it returns that character, updating the external variable optind and a static variable nextchar
       so that the next call to getopt() can resume the scan with the following option character or argv-element.

       If  there  are  no  more option characters, getopt() returns -1.  Then optind is the index in argv of the first argv-element that is not an
       option.

       optstring is a string containing the legitimate option characters.  If such a character is followed by a  colon,  the  option  requires	an
       argument,  so getopt places a pointer to the following text in the same argv-element, or the text of the following argv-element, in optarg.
       Two colons mean an option takes an optional arg; if there is text in the current argv-element, it is returned in optarg,  otherwise  optarg
       is  set	to  zero.   This  is  a GNU extension.	If optstring contains W followed by a semicolon, then -W foo is treated as the long option
       --foo.  (The -W option is reserved by POSIX.2 for implementation extensions.)  This behaviour  is  a  GNU  extension,  not  available  with
       libraries before GNU libc 2.

       By default, getopt() permutes the contents of argv as it scans, so that eventually all the non-options are at the end.  Two other modes are
       also implemented.  If the first character of optstring is `+' or the environment variable POSIXLY_CORRECT is set,  then	option	processing
       stops  as  soon	as a non-option argument is encountered.  If the first character of optstring is `-', then each non-option argv-element is
       handled as if it were the argument of an option with character code 1.  (This is used by programs that were written to expect  options  and
       other  argv-elements in any order and that care about the ordering of the two.)	The special argument `--' forces an end of option-scanning
       regardless of the scanning mode.

       If getopt() does not recognize an option character, it prints an error message to stderr, stores the character in optopt, and returns  `?'.
       The calling program may prevent the error message by setting opterr to 0.

       If  getopt()  finds  an option character in argv that was not included in optstring, or if it detects a missing option argument, it returns
       `?'  and sets the external variable optopt to the actual option character.  If the first character of optstring	is  a  colon  (`:'),  then
       getopt()  returns `:' instead of `?' to indicate a missing option argument.  If an error was detected, and the first character of optstring
       is not a colon, and the external variable opterr is nonzero (which is the default), getopt() prints an error message.

       The getopt_long() function works like getopt() except that it also accepts long options, started out by two dashes.  Long option names  may
       be abbreviated if the abbreviation is unique or is an exact match for some defined option.  A long option may take a parameter, of the form
       --arg=param or --arg param.

       longopts is a pointer to the first element of an array of struct option declared in <getopt.h> as

	  struct option {
	      const char *name;
	      int has_arg;
	      int *flag;
	      int val;
	  };

       The meanings of the different fields are:

       name   is the name of the long option.

       has_arg
	      is: no_argument (or 0) if the option does not take an argument, required_argument (or 1) if the  option  requires  an  argument,	or
	      optional_argument (or 2) if the option takes an optional argument.

       flag   specifies  how  results are returned for a long option.  If flag is NULL, then getopt_long() returns val.  (For example, the calling
	      program may set val to the equivalent short option character.)  Otherwise, getopt_long() returns 0, and flag points  to  a  variable
	      which is set to val if the option is found, but left unchanged if the option is not found.

       val    is the value to return, or to load into the variable pointed to by flag.

       The last element of the array has to be filled with zeroes.

       If longindex is not NULL, it points to a variable which is set to the index of the long option relative to longopts.

       getopt_long_only() is like getopt_long(), but `-' as well as `--' can indicate a long option.  If an option that starts with `-' (not `--')
       doesn't match a long option, but does match a short option, it is parsed as a short option instead.

RETURN VALUE

       The getopt() function returns the option character if the option was found successfully, `:' if there was a missing parameter  for  one	of
       the options, `?' for an unknown option character, or -1 for the end of the option list.

       getopt_long()  and  getopt_long_only()  also return the option character when a short option is recognized.  For a long option, they return
       val if flag is NULL, and 0 otherwise.  Error and -1 returns are the same as for getopt(), plus `?' for an ambiguous match or an	extraneous
       parameter.

ENVIRONMENT VARIABLES

       POSIXLY_CORRECT
	      If this is set, then option processing stops as soon as a non-option argument is encountered.

       _<PID>_GNU_nonoption_argv_flags_
	      This  variable  was  used by bash 2.0 to communicate to GNU libc which arguments are the results of wildcard expansion and so should
	      not be considered as options.  This behaviour was removed in bash version 2.01, but the support remains in GNU libc.

EXAMPLE

       The following example program illustrates the use of getopt_long() with most of its features.

       #include <stdio.h>     /* for printf */
       #include <stdlib.h>    /* for exit */
       #include <getopt.h>

       int
       main (int argc, char **argv) {
	   int c;
	   int digit_optind = 0;

	   while (1) {
	       int this_option_optind = optind ? optind : 1;
	       int option_index = 0;
	       static struct option long_options[] = {
		   {"add", 1, 0, 0},
		   {"append", 0, 0, 0},
		   {"delete", 1, 0, 0},
		   {"verbose", 0, 0, 0},
		   {"create", 1, 0, 'c'},
		   {"file", 1, 0, 0},
		   {0, 0, 0, 0}
	       };

	       c = getopt_long (argc, argv, "abc:d:012",
			long_options, &option_index);
	       if (c == -1)
		   break;

	       switch (c) {
	       case 0:
		   printf ("option %s", long_options[option_index].name);
		   if (optarg)
		       printf (" with arg %s", optarg);
		   printf ("
");
		   break;

	       case '0':
	       case '1':
	       case '2':
		   if (digit_optind != 0 && digit_optind != this_option_optind)
		     printf ("digits occur in two different argv-elements.
");
		   digit_optind = this_option_optind;
		   printf ("option %c
", c);
		   break;

	       case 'a':
		   printf ("option a
");
		   break;

	       case 'b':
		   printf ("option b
");
		   break;

	       case 'c':
		   printf ("option c with value `%s'
", optarg);
		   break;

	       case 'd':
		   printf ("option d with value `%s'
", optarg);
		   break;

	       case '?':
		   break;

	       default:
		   printf ("?? getopt returned character code 0%o ??
", c);
	       }
	   }

	   if (optind < argc) {
	       printf ("non-option ARGV-elements: ");
	       while (optind < argc)
		   printf ("%s ", argv[optind++]);
	       printf ("
");
	   }

	   exit (0);
       }

BUGS

       The POSIX.2 specification of getopt() has a technical error described in POSIX.2 Interpretation 150.  The GNU implementation (and  probably
       all other implementations) implements the correct behaviour rather than that specified.

CONFORMING TO

       getopt():
	      POSIX.2,	provided the environment variable POSIXLY_CORRECT is set.  Otherwise, the elements of argv aren't really const, because we
	      permute them.  We pretend they're const in the prototype to be compatible with other systems.

GNU
								    2002-02-16								 GETOPT(3)